Method for making filamentous mats



Sept. 1,1970

H. J. TAYLOR, JR

METHOD FOR MAKING FILAMENTOUS MATS Filed Nov. 18, 1966 INVENTOR. HAROLD J. 774m 0A, JR.

ATTORNEY United States Patent O 3,526,557 METHOD FOR MAKING FILAMENTOUS MATS Harold J. Taylor, Jr., Louisville, Ky., assignor to American Air filter Company, Inc., Louisville, Ky., a corporation of Delaware Filed Nov. 18, 1966, Ser. No. 595,492 Int. Cl. D04h 3/16 US. Cl. 156167 Claims ABSTRACT OF THE DISCLOSURE The present invention relates to expanded filamentous mats and more particularly relates to improved methods for controlling filament concentrations in selected portions of such mats, by application of selected binder compositions to the mat and softening the binder compositions in selected portions of the mat during processing to permit reorientation of filaments in the mat.

BACKGROUND OF THE INVENTION One method for making an expanded filamentous mat which is well known in the art includes traversing a filament feeding apparatus back and forth axially along a downturning edge of a horizontally disposed rotating drum and feeding filaments, for example molten glass, from the filament feeding apparatus to the rotating drum. Filaments are collected on the rotating drum and the filament feeding apparatus is traversed back and forth along the downturning edge of the drum a plurality of times at selected traversing speeds so the filaments are drawn to the rotating drum to form a condensed mat having overlying layers of filaments. Each layer of the condensed mat includes filaments lying in approximate parallelism and the filaments of adjacent layers cross each other. The condensed filamentous mat is cut from the drum as a planar condensed mat, which is then drawn in a direction generally transverse the lay of filaments to stretch the mat lengthwise so the individual filaments are separated. Because of the characteristic disposition of filaments in the condensed mat, some of the filaments in each layer curl during the drawing operation, and the curled filaments increase the thickness of each layer of the mat so the overall thickness of the expanded mat is greatl increased. The expanded mat is fluflYy, is much longer and much thicker than the original condensed mat, and the average filament concentration of the mat is decreased because of the separation of the filaments which occurs during the expansion.

For certain applications it is desirable to provide a definite filament concentration in selected portions of a filamentous mat and in some such applications it is desirable to manufacture filamentous mats which include a thin skin-like layer of very high filament concentration at a selected location within the mat. Such skin-like layers, or layers of high filament concentration, provide support and dimensional stability to the fluffy portions of the expanded mat having low filament concentration. When such a product is used to filter a fluid stream to remove particulate matter from the fluid stream, the skin-like layer of high filament concentration can advantageously facilitate the removal of extremely fine particles from the fluid stream.

SUMMARY OF THE INVENTION It has been recognized that the straightforward, advantageous method in accordance with the present invention provides means by which an expanded filamentous mat can be formed and the filament concentration in selected layers or at a selected location in the mat can be "ice controlled in a straightforward, economical manner without significant modification of conventional equipment.

In view of the present invention it is further recognized that a novel and advantageous method is provided for forming a compressed skin-like layer of extremely high filament concentration within an expanded mat whereby the location of the skin-like layer can be selected to provide desired characteristics in the finished product.

Various other features of the present invention will become obvious to one skilled in the art upon reading the disclosure set forth hereinafter.

In accordance with the present invention, an improved method is provided for making a portion of an expanded filamentous mat and controlling filament concentration in selected portions of the filamentous mat comprising: feeding filaments from filament feeder means to collector means; collecting the filaments on the collector means at selected angle of lay relative to a selected axis of the collector means to form a first portion of a condensed mat; spraying a selected first binder solution on the first portion; collecting filaments at selected angle of lay relative to the selected axis of the collector means to form a second portion of the mat; applying a second selected binder to the second portion of the condensed filamentous mat where the viscosity of the second binder is such that the viscosity of the binder on one portion of the mat is greater than the viscosity of the binder on the other portion of the mat at a selected temperature; stretching the filamentous mat, including the first and second portions, in a direction transverse to the general direction of lay of the filaments to separate the filaments and expanding the mat in the direction of thickness of the mat; heating the expanded mat to the selected temperature to decrease the viscosity of the binder on that portion having lower viscosity binder to permit reorientation of filaments of such portion while the binder in the other portion remains in a relatively more viscous condition to restrict reorientation of filaments of such portion; compressing the portion of the expanded mat having a lower viscosity a selected amount while the binder is in less viscous condition; and hardening the softened binder while that portion is in the compressed condition.

BRIEF DESCRIPTION OF THE DRAWINGS Referring to the drawings which disclose one advantageous embodiment of the present invention:

FIG. 1 shows a diagrammatic view of an apparatus for forming a condensed filamentous mat on a rotating drum;

FIG. 2 is a view taken along a plane passing through line 2-2 of FIG. 1;

FIG. 3 is a diagrammatic plan view pansion of a filamentous mat.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The apparatus for forming a condensed filamentous mat as shown in the examples of FIGS. 1 and 2 includes a filament feeder 1 which axially traverses a rotating drum 11, which can be rotated by means not shown, above and generally parallel to the down-turning edge of the drum. Filaments of selected material, for example molten glass, are fed from orifices (not shown) in the bottom of feeder 1 to be attenuated by and collected upon rotating drum 11. The orifices in the bottom of feeder 1 can be arranged in any desired geometric configuration, for example in longitudinally extending rows to feed filaments to the drum on a selected pattern. The diameter of filaments 15 drawn from feeder 1 to, drum 11 is influenced by the speed of rotation of drum 11, and the diameter and the temperature of the orifices.

In the example as shown in FIGS. 1 and 2, tracks 8 showing the exare provided above the down-turning edge of drum 11 and filament feeder 1 can be driven back and forth along tracks 8 in reciprocatory traverses. Feeder 1 is cooperatively attached to an endless chain 12 which is driven by a sprocket 3 turned by variable speed drive means 10. Endless chain 12 also turns around idler sprocket 7, Where sprockets 3 and 7 are mounted a selected distance apart and can advantageously be mounted at opposite ends of drum 11. Chain 12 is cooperatively joined to feeder 1 by means of a pin 13 which nests in a vertically extending pin-receiving slot 14 of arm 2 which is joined to filament feeder 1. Pin 13 is free to move in a vertical direction in slot 14 while filament feeder 1 moves in a generally horizontal direction along tracks 8 in response to movement of chain 12.

As feeder 1 is reciprocated back and forth above the down-turning edge of drum 11, pin 13 moves with chain 12 in one horizontal direction between sprockets 3 and 7 to drive filament feeder 1 accordingly. At the end of a feeder traverse, pin 13 reaches one of the sprockets, for example, sprocket 3, and moves around the sprocket in a generally vertical direction in slot 14 so there is relatively little horizontal movement of feeder 1 as pin 13 moves around sprocket 3. As pin 13 leaves sprocket 3, feeder 1 is driven at the same horizontal speed as chain 12 but in a direction opposite to the direction of travel before pin 13 passed around the sprocket. It Will be realized that a similar sequence of events occurs as pin 13 passes around each sprocket and therefore filament feeder 1 is driven back and forth along tracks 8 in reciprocatory traverses extending generally from sprocket 3 to sprocket 7 along the aforementioned down-turning edge of rotating drum 11.

The angle of lay of filaments deposited on drum 11, which is the same as the angle of lay of the filaments of the planar mat removed from the drum, can be measured as the angle between a transverse axis of the drum and the projection of filaments 15 on a plane passing longitudinally through the drum. The angle of lay is determined by the traversing speed of feeder 1 along the down-turning edge of drum 11 relative to the rotational speed of drum 11. It will be noted that the angle of lay of filaments 15 is measured in a first quadrant for those filaments deposited on drum 11 as feeder 1 traverses drum 11 in one direction and when the direction of travel of feeder 1 is in an opposite direction the angle of lay is measured in a mirror quadrant. "It will, therefore, be understood that if the linear traversing speed of feeder 1 is the same for successive traverses in opposite directions along drum 11, the angle of lay of the filaments deposited on drum 11 is the same, even though the angles are measured in mirror quadrants for adjacent filament layers.

Assuming no change in speed of rotation of drum 11, the angle of lay of filaments deposited on drum 11 can be selectively changed by varying the linear traversing speed of feeder 1. Increasing the feeder traversing speed increases the angle of lay of filaments on the drum, and therefore the angle of lay of filaments of the fully formed condensed planar mat subsequently removed from the drum. The angle of lay of the filaments in the planar mat determines the length to which the planar mat can be stretched during an expansion step where the mat is drawn in a direction transverse the lay of the filaments, and as is known in the art, the greater the angle of lay of filaments in the planar mat the shorter the ultimate length of the stretched mat. During the stretching operation, the filaments of each layer of the condensed mat first separate and buckle or curl so the mat expands in thickness. If the mat is stretched far enough, the filaments or layers of filaments are stretched to their ultimate length, which is determined by the angle of lay of filaments in the condensed mat before expansion, and the filaments are drawn straight. The straightened filaments lose their curled configuration. Filaments in other layers or portions of the mat which were deposited at lesser angles of lay than the straightened filaments are not drawn to their ultimate length and remain curled to provide expanded fluffy portions of the expanded mat. If a condensed mat including layers of filaments at different angles of lay is expanded until the filaments deposited at the greater angles of lay are drawn to their ultimate length and are straightened, the resulting mat includes thin layers of substantially straightened filaments and fiuffy layers of curled filaments corresponding to layers of filaments deposited at lesser angles of lay which are not straightened during the expansion.

In one feature of the method in accordance with the present invention, a filamentous mat is formed on a collecting means, for example, a rotating drum as shown in FIGS. 1 and 2, and different layers of the mat are sprayed with different advantageously selected binder substances. The binder can be applied, for example, by a sprayer 18 which traverses the drum during the deposition of the filaments. By the method of the present invention, the condensed mat can include filaments at only one angle of lay and the desired characteristics can be obtained by proper manipulation of the binder system or the mat formed on the drum can include layers of fila ments at different angles of lay.

In one example, a condensed mat can be formed on drum 11 to include one first portion including at least one layer deposited when feeder 1 traverses drum 11 at a relatively high rate of speed so the filaments are deposited on drum 11 at a first angle of lay. The first portion is sprayed with a binder solution having a selected viscosity-temperature relationship. A second portion of the filamentous mat, including at least one layer of filaments, is then formed when the filament feeder traverses the rotating drum at relatively loW rate of speed, less than the average speed of the filament feeder during the formation of the first portion of the mat, so filaments are deposited at a lower angle of lay. The second formed portion of the filamentous mat is sprayed with a second selected binder also having a selected viscosity-temperature relationship. In accordance with one feature of the present invention, the relative viscosity relationship of the different binders is such that at a selected temperature the viscosity of one binder, the second binder in this example, is significantly greater than the viscosity of the other binder, in this example the first binder so that at the selected temperature, the first binder is softened to permit reorientation of filaments in the first formed portion of the filamentous mat While the second binder is in a relatively more viscous condition to restrict movement of filaments of the second portion.

It is to be noted that the second formed portion of the mat can also include groups of filaments formed by periodically stopping the traversing motion of feeder 1 during the formation of the second portion of the filamentous mat so filaments are drawn directly to the rotating drum at essentially zero angle of lay and fall on top of themselves in contiguous relation. The strands so formed are composed of multi filaments and remain grouped in the form of multi-filament strands throughout the further processing of the mat. The grouped filaments can be considered as monofilaments which decrease the apparent average filament concentration of the expanded mat and can be selectively distributed throughout the mat to control the filament density in selected portions of the mat.

In accordance with one feature of the present invention, the binder applied to a selected portion of the mat during the formation of the condensed mat is softened after the mat is expanded to allow filaments of that portion to be freely or selectively reoriented. While the binder in one portion of the mat is softened, the binder in another portion of the mat is maintained in a relatively viscous condition to hold the filaments in their expanded orientation. In the example of FIG. 3, mat 20 is stretched to expand the mat as hereinbefore described and the expanded mat is passed through an oven 28 on a conveyor 23. The binder in one portion of the mat is softened to allow reorientation of the filaments in the one portion while the binder in the other portion of the filamentous mat remains in a highly viscous condition to prevent the reorientation of the filaments of the second portion. The binder on the one portion which advantageously is softened at the selected temperature and is used in the formation of the one portion of the filamentous mat, can be, for example, composed of the reaction product of 1.7 parts of urea with one part of formaldehyde in a solution with solids concentration approximately 65%. The binder on the other portion used in the formation of the other portion of the mat which has a higher viscosity at the selected temperature can for example be of the same general composition but with a higher solids concentration so the viscosity is higher at the selected temperature. The binder on the other portion can also be a thermosetting composition which is advantageously thermally reacted at the selected temperature while the binder on the one portion is softened.

The filamentous mat, including the one and the other formed portions, can be cut parallel to the longitudinal axis of drum 11 and removed from the drum as a con densed mat 20. In the example of the figures mat 20 includes at least one portion, or number of layers 21, deposited on drum 11 at increased angle of lay, and at least one portion, or number of layers 22, deposited at lesser angles of lay. Mat 20 can be drawn by hand or other suitable means in a direction transverse the general direction of lay of the filaments in the mat and during the stretching operation, mat 20 is lengthened in the direction of draw so the filaments curl and the thickness of the mat 20 is increased to form an expanded mat 29. Expanded mat 29 includes expanded portion 21a, which results from the expansion of layer 21, and a portion 22a resulting from the expansion of portion 22 of mat. The expanded thickness of portion 21a is less than the expanded thickness of portion 22a because the increased angle of lay of filaments in portion 21 permits less curling and expansion than is experienced by layers 22 deposited on drum 11 at lesser angle of lay.

An expanded filamentous mat in accordance with the present invention can include only curled fibers, or, as hereinbefore described where it is desired to form a skin-like layer in the final product, the condensed mat can include selectively distributed layers of straightened filaments. When this procedure is followed, the resulting stretched mat includes expanded layer of curly filaments and selectively distributed, relatively thin, layers of generally straight filaments.

In the example of the present invention, as shown in FIG. 3, oven 28 includes heat source 27 to heat the expanded mat to the selected temperature so the binder in the first portion 21a is softened, and in accordance with one feature of the present invention, the filaments of the portion of the expanded mat including the softened binder are reoriented while the binder is in softened condition. In the example of FIG. 3, if mat 20 is not stretched to the ultimate length of the filaments of portion 21 the filaments of layer 21a can be compressed to selectively decrease the thickness of layers 21a. FIG. 3 is an illustration of an example where the filaments of the expanded mat are not stretched to the ultimate length so there is compression of layers 21a when the binder is softened.

At 24 the binder in portion 21a begins to soften and compression begins as shown by the decreasing thickness of layer 21a. At point 26, as indicated, the binder has been softened and compression is complete so that the filamentout mat emitted from oven 28 includes an expanded portion 22a and a compressed portion 21a. Compression means can be provided to facilitate compression of the mat, or, it has been recognized that by the method in accordance with the present invention as shown in the example of FIG. 3, the weight of layers 22a can be utilized to provide the compressive force necessary to decrease the thickness of portion 21 a selected degree so additional equipment is not necessary to accomplish the compression.

If the filaments of layer 21a of expanded mat 29 have been stretched to their ultimate length, softening the binder facilitates reorientation of the already essentially straight filaments to provide more uniform configuration and distribution so there is correspondingly less decrease in the thickness during compression.

After the compression of the filamentous mat, the binder can be hardened in a convenient manner, for example, by heating the binder (to cure the resin) or by cooling the binder to permit solidification. The filamentous mat is then packaged for further processing.

The invention claimed is:

1. An improved method for making expanded filamentous mat comprising: feeding filaments from filament feeding means to filament collector means; collecting filaments on said collector means at selected angle of lay relative to a selected axis of said collector means to form a first portion of a condensed filamentous mat; spraying first binder solution on said first portion of said condensed filamentous mat; collecting filaments on said filament collecting means at second selected angle of lay relative to said selected axis of said collector means to form a second portion of said condensed filamentous mat; applying a selected second binder to said second portion of said condensed filamentous mat wherein the viscosity of said second binder is sufficiently different that the viscosity of the binder on one portion of the mat is greater than the viscosity of the binder on the other portion of the mat at selected temperature; releasing said condensed filamentous mat from said collector means to form a planar mat; stretching said planar mat in a direction transverse the general direction of lay of said filaments to separate said filaments so some of said filaments curl and expand the thickness of said mat to form an expanded filamentous mat; heating said expanded mat to said selected temperature to soften said binder on one portion of said mat; reorienting filaments of said portion of said mat where said binder is softened; and hardening said softened binder.

2. The method of claim 1 wherein said first angle of lay and said second angle of lay are equal.

3. The method of claim 1 including spraying said second portion of said mat with second binder having viscosity greater than the viscosity of said first binder at said selected temperature.

4. The method of claim 3 including heating said expanded mat to said selected temperature to soften said binder in said first portion of said mat, compressing said first portion while said binder in said first portion is in softened condition; and, hardening said first binder to maintain said first portion in compressed condition.

5. The method of claim 3 wherein said first angle of lay is greater than said second angle of lay.

6. The method of claim 5 including stretching said condensed mat in a direction transverse the direction of lay of filaments of said condensed mat until filaments of said first portion are straightened and filaments of said second portion remain in curled configuration.

7. An improved method for making an expanded filamentous mat comprising: feeding filaments from filament feeder means to drum means; rotating said drum means; reciprocating said feeder means longitudinaly back and forth along a down-turning edge of said rotating drum to distribute filaments longitudinally along said rotating drum so said filaments are collected upon said rotating drum as said feeder means is reciprocated back and forth in successive traverses along said down-turning edge of said rotating drum; spraying a first portion of said condensed mat formed on said rotating drum with a first selected binder; spraying a second portion of said filamentous mat collected on said rotating drum with a second selected binder where the viscosity of said first and selected binders at selected temperature is sufficiently different that the viscosity of a binder on one portion of said mat is greater than binder on the other portion of said mat at selected temperature; slitting said mat axially of said drum and removing said mat from said drum as a condensed planar mat; stretching said filamentous mat in a direction generally transverse to the direction of lay of filaments of said planar mat to expand said condensed mat to form an expanded mat including expanded first and second portion; heating said filamentous mat to said selected temperature so said binder in one portion of said mat remains in a relatively more viscous condition; reorienting filaments in the portion of said mat Where said binder is softened, and hardening said softened binder.

8. The method of claim 7 wherein said second binder has a viscosity greater than the viscosity of said first binder at said selceted temperature.

9. The method of claim 8 including traversing said filament feeder means at a relatively greater speed during the formation of said first portion than during the formation of said second portion so the angle of lay of filaments collected on said drum during formation of said first portion is greater than the average angle of lay of filaments of said second portion; stretching said filamentous mat 8 until filaments of said first portion are drawn straight; heating said expanded filamentous mat to said selected temperature to soften the binder of said first portion, while binder in said second portion remains in relatively viscous condition; and hardening said binder in said first portion.

10. The method of claim 8 including heating said expanded mat to said selected temperature to soften said binder in said first portion; compressing said first portion a selected amount to decrease the thickness of said first portion; and hardening said binder in said first portion to retain said first portion in compressed condition.

References Cited UNITED STATES PATENTS 2,505,045 4/1950 Holcomb 156-16 7 3,051,602 8/ 1962 Schairbaum 156-167 3,438,587 4/1969 Jackson n 156167 CARL D. QUARFORTH, Primary Examiner B. H. HUNT, Assistant Examiner U.S.v Cl. X.R. 156-174 

